1. Field of the Invention
The present invention relates to electromagnetic contactors for making and breaking a circuit. In particular, the invention relates to an electromagnetic contactor that has the ability to detect contactor condition through a sensing circuit indicating contactor status.
2. Background of the Invention
Electromagnetic contactors are used in a variety of applications where it is desired that a circuit be made or broken in response to an electric signal. An example application is the use of power contactors in computer systems.
Although contactors are generally reliable, there is frequently a need to verify that contacts have actually been closed in response to the electric signal. Certain failures of the circuit or of the contactor components could result in a failure to close. Fault isolation and diagnosis require a means of sensing the position of the contacts of the contactor assembly to determine their response to a closure signal.
Contactor manufacturers have addressed this need for closure verification by adding a mechanical switch to contactors that is activated by contactor closure. For example, a tab can be located on the power contactor moving contacts and that tab can strike a mechanical switch mounted on the same body as the contactor forming a mechanically closed circuit. A fault isolation or diagnosis circuit can be used to test the status of mechanical switches to verify operation of contactors in response to signals.
The use of mechanical switches increases manufacturing cost and reduces reliability. Mechanical switches are costly to manufacture and install in conjunction with the contactors. In addition, because the switches are mechanical, they are subject to failure due to repeated use. Thus, the use of mechanical switches can lead to diagnostic failures caused by the switch as well as by a contactor failure.
Some manufacturers have suggested mechanisms for sensing the closure of electromagnetic contactors by sensing the wave forms generated by the closure movement. Systems of this type have the disadvantage that they can sense only the movement of the closure and cannot sense the steady state position of the contactors.